Small field-of-view imaging may be used to image small objects and/or an organ-of-interests within larger objects. When used to image an organ of interest, the data in the regions of the image other than the organ of interest regions can be truncated. This operation can introduce truncation artifacts into the images. These truncation artifacts are caused by parts of the object and/or the image being truncated on some of the projection images.
Artifacts may result during the reconstruction of the projection images into a three-dimensional tomography image, since these parts of the object are in some projection images, but not others. This can in turn limit the quantitative accuracy of the image of the organ of interest.
In cardiac SPECT, using small field of view systems has certain advantages over using large field of view systems. Imaging using small field of view systems may truncate the organ-of-interest (the patient's heart in cardiac SPECT), and also may truncate other regions. This truncation can introduce a truncation artifact into the image set, and can also limit the quantitative accuracy of the images.
For example, if the emission field of view is too small, even though one can use a truncation-free attenuation map for attenuation correction, often one cannot get quantitatively accurate attenuation corrected images of the heart.
Techniques have been proposed to reduce the truncation artifacts. One technique suggests modifying the back projection. This may be used in iterative reconstruction algorithms. In this technique, regions of the image corresponding to the truncation in the projection data are not updated for that particular angle.
A complex conjugate concept can be used with the assumption of the body symmetry for truncation compensation in transmission scans.
Data completion techniques can be used to estimate the data in the truncated regions.
These truncation compensation techniques may improve the quantitative accuracy of the images themselves as compared to the images without truncation compensation.
However, when the field of view is very small, none of these techniques may be effective.
For example, for SPECT imaging, the organ of interest may be the heart. The heart often cannot be imaged accurately using very small fields of views, such as 15.0 cm, using the prior art techniques.